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Tess Vigeland: All those holiday deals being offered by Detroit automakers, yeah, they pale in comparison to the Nano, from India's Tata Motors; it'll be the cheapest car in the world, if it ever gets released. It was announced with great fanfare back in January, but since then, it's been plagued by everything from the slumping economy to protests from farmers after Tata built a Nano factory on their land. An October release date got pushed to this month and now it's been pushed again, to March of next year. Some Indians wouldn't mind even more delays, though. They worry a wave of Nanos could make their bad urban pollution worse -- not the kind of pollution you'd think though. Marketplace's Rico Gagliano explains.

Rico Gagliano: At a truck stop on the outskirts of Mumbai, truckers lovingly work on their vehicles. Every truck is hand-painted in bright colors; they look like circus caravans. And on the back bumper of every single one are painted the words: "HORN OK PLEASE." I asked trucker Sayek Nazir why.

That may have been true once, but these days, the sign seems more like just a tradition, because in today's India, drivers basically never stop honking.

This is Mumbai on a Friday night, and it's not even as bad as Indian city noise can get -- Mumbai laws at least prohibit the use of air horns. Which sound like this:

[Air horn]

My God, that is loud!

Air horn laws aren't always enforced, though. And the fear is if tons of super-cheap Nanos start rolling onto clogged Indian streets, horn use of every stripe could reach brain-shattering proportions.

Vipul Shah: I believe it's in Indians' culture and psychology to make noise wherever they are.

Vipul Shah is a recent business administration grad in the Indian city of Pune. A few years ago he returned home from studying in relatively silent England.

Shah: The first thing I noticed was tremendous amount of noise here and that was intolerable. And I initiated a campaign called "Quiet India" campaign. and our motto is "Horn Not OK Please."

Last year, he got national media attention by putting the "Horn Not OK" slogan on a T-shirt and taking a 75-mile bike trip. The campaign staged student rallies in several cities. Pune's mayor kicked off the first one with a speech, and traffic cops were big boosters, too.

Shah: They were like, "Oh, you're doing it for us, actually," because they're the ones who actually suffer from the noise pollution. And the rickshaw drivers.

That's surprising, since in my experience, rickshaw drivers -- they pilot little three-wheeled open-air taxis -- honk more than almost anyone in the country.

Gagliano: So the rickshaws actually like this idea.

Shah: Definitely. It's actually, one of the researchers has revealed one third of the rickshaw drivers suffer hearing loss after driving for several years on the roads.

Sharad Rao: Yeah, it is true.

Sharad Rao is President of Mumbai's Autorickshaw Union. He agrees horn noise leaves his drivers' ears ringing. But does he think a bunch of students from Pune have actually made horn use not OK?

Rao: I welcome the campaign by the Pune youngsters. But until there is some restriction on vehicle numbers, the horn use is not going to be stopped.

Gagliano: Is it possible to keep vehicular traffic down?

Rao: Impossible. I don't believe in it.

And why should he? Last April an official "no honking" day in Mumbai seemed to fall on deaf ears. Despite an ad campaign featuring Bollywood celebrities, and despite the threat of a traffic ticket, the city's drivers honked pretty much as usual.

Meanwhile, the U.N. projects by 2015, Mumbai alone will be home to 22 million people -- more than almost any urban area on Earth. More and more of them will be driving cars.